That said, there might be ways to record sound from the microphone of a computer / tablet / smartphone, via Javascript or something.
But this has little to do with Limesurvey, you would need to do some research on that.
In any way, the browser will most probably ask the interviewer if they allow the use of the microphone. Of course this is a good thing, because depending on where you are located, there is a high probability that recording someone without consent is illegal (not sure how to read "behind the scenes"). No matter if technically possible or legal/illegal: you should definitely inform the interviewer (who should inform the interviewee) about the recording.
Help us to help you!
Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.